1. Field of the Invention
The present invention relates to a method and to an apparatus for adjusting a definite position of rest of a rotary tube, particularly of a tube mill, by means of terminating energization of the drive.
2. Description of the Prior Art
The adjustment of a definite position of rest of a rotary tube, particularly of a tube mill, becomes necessary in the case of standstill for the purpose of operation and maintenance of the mill, particularly of the inner chamber of the mill. In addition, the maintenance of a definite position in the case of the so-called interval rotation in the starting position is of importance for the prevention of deformations of the tube caused by temperature and tension. If in particular a mill is shut off from normal operation, then tensions occur in the mill tube, which with long tubes (for example cement mills) may lead to appreciable damages, in that the filling of the grinding body maintains the temperature derived from the grinding process for a longer time, while the surface of the tube which is not covered by grinding bodies transmits the heat relatively quickly into the surrounding environment. Between the upper portion and the lower portion of the tube, under these circumstances, a temperature difference arises, which together with the one-sided load may lead to permanent deformation of the tube.
In order to attain a uniform protective cooling of the mill tube, the mill tube must therefore, after termination of normal operation, be rotated over a longer period of time, for example 6 hours at intervals of, for example, 30 minutes each, over a predetermined angle. With the state of the art, it is conventional to equip the mill for this purpose, in particular, with an auxiliary drive. Advantageously, in this connection, the magnetic flux of the auxiliary drive is fed through the main drive, because in this case the auxiliary drive, due to the relatively high total translation is to be provided only for a relatively low torsional or twisting moment, for which reason its costs do not exceed approximately 10% of the main drive.
Apart from this expenditure of the auxiliary drive, necessary only for unproductive measures, it is found as a further disadvantage that its maintenance and servicing upon connection and disconnection, as well as its upkeep, imposes particular responsibilities on the operating and maintenance personnel.
In addition to this, however, further difficulties arise from the auxiliary drive with slowly-traveling driving motors, as the latter are frequently encountered at the present time. The expenditure and costs for an auxiliary drive having comparible output are increased in many cases in relation to the torsional or twisting moments.